. >> reporter: nato did not say whether this was another in a series of insider attacks where afghan security forces turned on coalition troops. the so-called green on blue attacks have left at least 52 international forces dead this year. the u.s. commander in afghanistan told 60 minutes lara logan he's angry some afghan troops have turned on americans who trained them. >> i'm mad as hell to be honest with you. we're willing to sacrifice a lot for this campaign but not willing to be murdered for it. >> reporter: the attacks also frustrate afghan's president amad karzai. >> these attacks are sad. it's something i have discussed in detail, something that i take responsibility to correct. >> reporter: these incidents are a serious threat to the u.s. mission in afghanistan. drew levinson, cbs news. >> joint operations between u.s. and afghanistan forces resumed recently after being suspended two weeks ago. most american troops are scheduled to be out of afghanistan by the end of 2014. >>> today the power plant in alexandria, virginia right on the potomac river will officially shut down.